From 65d0f0122610de5176249642fac74f0bfe2ce0d1 Mon Sep 17 00:00:00 2001
From: Nick <73077675+tmzane@users.noreply.github.com>
Date: Tue, 12 May 2026 11:54:57 +0300
Subject: [PATCH 1/2] feat: rename module, add slogattr

---
 README.md                                  | 14 ++--
 go.mod                                     |  2 +-
 slogattr/attr.go                           | 61 ++++++++++++++++++
 slogattr/attr_test.go                      | 74 ++++++++++++++++++++++
 context.go => slogctx/context.go           |  1 +
 handler.go => slogctx/handler.go           |  0
 handler_test.go => slogctx/handler_test.go | 12 ++--
 7 files changed, 148 insertions(+), 16 deletions(-)
 create mode 100644 slogattr/attr.go
 create mode 100644 slogattr/attr_test.go
 rename context.go => slogctx/context.go (87%)
 rename handler.go => slogctx/handler.go (100%)
 rename handler_test.go => slogctx/handler_test.go (88%)

diff --git a/README.md b/README.md
index 6f4dc50..a2ec239 100644
--- a/README.md
+++ b/README.md
@@ -1,17 +1,13 @@
-# slogctx
+# slogutil
 
-[![checks](https://github.com/go-simpler/slogctx/actions/workflows/checks.yaml/badge.svg)](https://github.com/go-simpler/slogctx/actions/workflows/checks.yaml)
-[![docs](https://pkg.go.dev/badge/go-simpler.org/slogctx.svg)](https://pkg.go.dev/go-simpler.org/slogctx)
-[![codecov](https://codecov.io/gh/go-simpler/slogctx/branch/main/graph/badge.svg)](https://codecov.io/gh/go-simpler/slogctx)
+[![checks](https://github.com/go-simpler/slogutil/actions/workflows/checks.yaml/badge.svg)](https://github.com/go-simpler/slogutil/actions/workflows/checks.yaml)
+[![docs](https://pkg.go.dev/badge/go-simpler.org/slogutil.svg)](https://pkg.go.dev/go-simpler.org/slogutil)
+[![codecov](https://codecov.io/gh/go-simpler/slogutil/branch/main/graph/badge.svg)](https://codecov.io/gh/go-simpler/slogutil)
 
 ## Install
 
 Go 1.25+
 
 ```shell
-go get go-simpler.org/slogctx
+go get go-simpler.org/slogutil
 ```
-
-## Usage
-
-See [tests](handler_test.go).
diff --git a/go.mod b/go.mod
index 91f2153..55bec45 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
-module go-simpler.org/slogctx
+module go-simpler.org/slogutil
 
 go 1.25.0
diff --git a/slogattr/attr.go b/slogattr/attr.go
new file mode 100644
index 0000000..35d1f97
--- /dev/null
+++ b/slogattr/attr.go
@@ -0,0 +1,61 @@
+// Package slogattr implements utilities for creating [slog.Attr]s.
+package slogattr
+
+import (
+	"cmp"
+	"fmt"
+	"log/slog"
+	"strconv"
+)
+
+// ErrorKey is the key used by the [Error] function.
+// The associated value is an [error].
+const ErrorKey = "error"
+
+// Error returns a [slog.Attr] for an [error] value.
+func Error(err error) slog.Attr {
+	return slog.Any(ErrorKey, err)
+}
+
+// Slice returns a [slog.Attr] for a slice of [cmp.Ordered] values.
+func Slice[T cmp.Ordered](key string, ts []T) slog.Attr {
+	return slog.Any(key, ts)
+}
+
+// Stringer returns a [slog.Attr] for an [fmt.Stringer] value.
+func Stringer(key string, s fmt.Stringer) slog.Attr {
+	return slog.Any(key, s)
+}
+
+// LogValuer returns a [slog.Attr] for a [slog.LogValuer] value.
+func LogValuer(key string, v slog.LogValuer) slog.Attr {
+	return slog.Any(key, v)
+}
+
+// LogValuers returns a [slog.Attr] for a slice of [slog.LogValuer] values.
+// Given to [slog.JSONHandler], it will be written as {"key":{"1":...,"2":...}},
+// where ... is the [slog.LogValuer] itself.
+func LogValuers[T slog.LogValuer](key string, ts []T) slog.Attr {
+	// A [slog.LogValuer] in a slice is not supported by [log/slog].
+	// As a workaround, we convert the slice into a [slog.GroupValue].
+	// More:
+	// - https://github.com/golang/go/issues/63204
+	// - https://github.com/golang/go/issues/71088
+	attrs := make([]slog.Attr, len(ts))
+	for i := range ts {
+		attrs[i] = slog.Any(strconv.Itoa(i+1), ts[i])
+	}
+	return slog.Attr{Key: key, Value: slog.GroupValue(attrs...)}
+}
+
+// Lazy returns a [slog.Attr] for a lazily evaluated [cmp.Ordered] value.
+func Lazy[T cmp.Ordered](key string, fn func() T) slog.Attr {
+	return slog.Any(key, lazy[T](fn))
+}
+
+type lazy[T cmp.Ordered] func() T
+
+// LogValue implements [slog.LogValuer].
+func (l lazy[T]) LogValue() slog.Value {
+	return slog.AnyValue(l())
+}
diff --git a/slogattr/attr_test.go b/slogattr/attr_test.go
new file mode 100644
index 0000000..505970d
--- /dev/null
+++ b/slogattr/attr_test.go
@@ -0,0 +1,74 @@
+package slogattr_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"log/slog"
+	"testing"
+
+	"go-simpler.org/slogutil/slogattr"
+)
+
+func TestAll(t *testing.T) {
+	replaceAttr := func(_ []string, a slog.Attr) slog.Attr {
+		if a.Key == slog.TimeKey || a.Key == slog.LevelKey || a.Key == slog.MessageKey {
+			return slog.Attr{}
+		}
+		return a
+	}
+
+	var buf bytes.Buffer
+	h := slog.NewJSONHandler(&buf, &slog.HandlerOptions{ReplaceAttr: replaceAttr})
+	l := slog.New(h)
+
+	l.Info("",
+		slogattr.Error(errors.New("oops")),
+		slogattr.Slice("slice", []int{1, 2, 3}),
+		slogattr.Stringer("stringer", slog.LevelInfo),
+		slogattr.LogValuer("log_valuer", point{1, 2}),
+		slogattr.LogValuers("log_valuers", []point{{1, 2}, {3, 4}}),
+		slogattr.Lazy("lazy", func() string { return "foo" + "bar" }),
+	)
+
+	var got bytes.Buffer
+	json.Indent(&got, buf.Bytes(), "", "  ")
+
+	const want = `{
+  "error": "oops",
+  "slice": [
+    1,
+    2,
+    3
+  ],
+  "stringer": "INFO",
+  "log_valuer": {
+    "x": 1,
+    "y": 2
+  },
+  "log_valuers": {
+    "1": {
+      "x": 1,
+      "y": 2
+    },
+    "2": {
+      "x": 3,
+      "y": 4
+    }
+  },
+  "lazy": "foobar"
+}
+`
+	if got.String() != want {
+		t.Errorf("\ngot: %s\nwant: %s", &got, want)
+	}
+}
+
+type point struct{ x, y int }
+
+func (p point) LogValue() slog.Value {
+	return slog.GroupValue(
+		slog.Int("x", p.x),
+		slog.Int("y", p.y),
+	)
+}
diff --git a/context.go b/slogctx/context.go
similarity index 87%
rename from context.go
rename to slogctx/context.go
index 26a0671..c5e0cce 100644
--- a/context.go
+++ b/slogctx/context.go
@@ -1,3 +1,4 @@
+// Package slogctx implements utilities for logging request-scoped data via [context.Context].
 package slogctx
 
 import (
diff --git a/handler.go b/slogctx/handler.go
similarity index 100%
rename from handler.go
rename to slogctx/handler.go
diff --git a/handler_test.go b/slogctx/handler_test.go
similarity index 88%
rename from handler_test.go
rename to slogctx/handler_test.go
index daf06f4..5f98175 100644
--- a/handler_test.go
+++ b/slogctx/handler_test.go
@@ -6,12 +6,12 @@ import (
 	"log/slog"
 	"testing"
 
-	"go-simpler.org/slogctx"
+	"go-simpler.org/slogutil/slogctx"
 )
 
 func TestHandler(t *testing.T) {
 	replaceAttr := func(_ []string, a slog.Attr) slog.Attr {
-		if a.Key == slog.TimeKey {
+		if a.Key == slog.TimeKey || a.Key == slog.LevelKey {
 			return slog.Attr{}
 		}
 		return a
@@ -29,9 +29,9 @@ func TestHandler(t *testing.T) {
 
 	got := "\n" + buf.String()
 	want := `
-level=INFO msg="adding foo"
-level=INFO msg="adding bar" foo=1
-level=INFO msg="got foo bar" foo=1 bar=2
+msg="adding foo"
+msg="adding bar" foo=1
+msg="got foo bar" foo=1 bar=2
 `
 	if got != want {
 		t.Errorf("\ngot: %s\nwant: %s", got, want)
@@ -51,7 +51,7 @@ func bar(ctx context.Context, l *slog.Logger) {
 
 // goos: darwin
 // goarch: arm64
-// pkg: go-simpler.org/slogctx
+// pkg: go-simpler.org/slogutil/slogutil
 // cpu: Apple M1 Pro
 // BenchmarkHandler/enabled-8              204999273                5.743 ns/op           0 B/op          0 allocs/op
 // BenchmarkHandler/disabled-8             261334262                4.591 ns/op           0 B/op          0 allocs/op

From ababed5018bb2fe38ac698988ab39f5b9e275d3b Mon Sep 17 00:00:00 2001
From: Nick <73077675+tmzane@users.noreply.github.com>
Date: Tue, 12 May 2026 11:57:45 +0300
Subject: [PATCH 2/2] fmt

---
 slogattr/attr_test.go   | 2 +-
 slogctx/handler_test.go | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/slogattr/attr_test.go b/slogattr/attr_test.go
index 505970d..1654074 100644
--- a/slogattr/attr_test.go
+++ b/slogattr/attr_test.go
@@ -32,7 +32,7 @@ func TestAll(t *testing.T) {
 	)
 
 	var got bytes.Buffer
-	json.Indent(&got, buf.Bytes(), "", "  ")
+	_ = json.Indent(&got, buf.Bytes(), "", "  ")
 
 	const want = `{
   "error": "oops",
diff --git a/slogctx/handler_test.go b/slogctx/handler_test.go
index 5f98175..5cb405e 100644
--- a/slogctx/handler_test.go
+++ b/slogctx/handler_test.go
@@ -46,7 +46,7 @@ func foo(ctx context.Context, l *slog.Logger) {
 
 func bar(ctx context.Context, l *slog.Logger) {
 	l.InfoContext(ctx, "adding bar")
-	ctx = slogctx.With(ctx, "bar", 2)
+	_ = slogctx.With(ctx, "bar", 2)
 }
 
 // goos: darwin